Harmonics Emissions and Power System Grid Resilience in Electric Vehicle Charging

Abstract

This chapter focuses on the harmonics emissions and power system grid resilience in electric vehicle (EV) charging. With the increasing demand for EVs, understanding the effects of harmonics on grid stability is critical. Converters in EV charging operations can contribute to high harmonics levels, causing disturbances and stressing the power system. The scope of the chapter encompasses challenges related to harmonics and emphasizes the need to ensure grid resilience. It also highlights the importance of understanding the correlations between harmonics emissions, operational parameters, and the increasing adoption of electric vehicle charging. This chapter also aims to discuss and present various harmonic mitigation techniques that can enhance power quality in electric vehicle integration.

1. Introduction

The surge in carbon dioxide emissions and volatile oil prices have opened doors for alternative technologies like electric vehicles (EVs). By harnessing sustainable green energy, the electrification of transportation presents a viable solution to address the goal of reducing greenhouse gas emissions. Electric vehicles offer the advantage of zero emissions and high energy conversion efficiency, setting them apart from conventional combustion engines. However, the rapid integration of EVs can pose a significant challenge to existing electric distribution systems, compounded by the current insufficiency of EV charging infrastructure.

The widespread adoption of electric vehicles globally has considerable momentum as a key solution to addressing environmental issues and reducing fuel dependency in the transport sector [1]. In 2022, Europe witnessed a significant growth in EV registrations, reaching a total of 1,729,000 vehicles, marking a 7% increase compared to the previous year [2]. European governments have implemented a range of incentives to support and accelerate the expansion of EVs, aiming for high levels of penetration. For instance, Spain has set an ambitious target of reaching 4 million electric vehicles by 2030 [3], which will contribute to a substantial surge in EV adoption in the coming years. The growing demand market for electric vehicles as a more environmentally friendly transportation option has raised concerns about the impact of charging these vehicles on electric grids.

In the near future, it is anticipated that the penetration of EVs into low-voltage residential networks will rise significantly. Due to its ease and the lack of charging infrastructure, overnight home charging is anticipated to be preferred by EV buyers. Due to the high penetration rates of EV charging stations and the growing number of EVs, the power infrastructure is currently facing enormous challenges. Consequently, a technical analysis of how EV charging affects the distribution system is necessary. EVs are becoming more and more popular every year, and they will soon supplant the current transportation system. To effectively plan for and accommodate this growing EV load while maintaining power quality, detailed technical studies of the impact of EV charging on the distribution system become imperative [4, 5]. These plans and research should include a precise evaluation of the EV load and its effects on power quality indices to facilitate efficient infrastructure planning. Manufacturers, consumers, and researchers all share a keen interest in the development of electric vehicles and their relationship with grid infrastructure. The integration of electric cars into distribution networks introduces several power quality concerns, with harmonic emissions being a notable issue. These challenges become particularly pronounced in scenarios with a high percentage of electric vehicle penetration, taking into account the clustering effect during the charging process [6].

The current capacity of electrical distribution systems is not projected to sufficiently accommodate such a rapid influx of EV penetration. Moreover, the integration of EVs into the distribution network has adverse effects on power quality due to the harmonics generated by these vehicles. In situations where loads exhibit non-linear behavior, drawing current in non-sinusoidal and distorted waveforms while connected to the network, has a detrimental impact on public networks designed to operate with sinusoidal voltage at rated power. These non-linear loads result in the creation of harmonics, leading to voltage distortion for customers, increased mechanical stress, confusion among protection equipment, and decreased efficiency of system components. EVs introduce harmonics into electrical systems through their non-linear charging behavior. Despite efforts to improve power electronics circuits and power factor correction, the harmonics generated by EV chargers are expected to be significant due to the high charging currents. Therefore, addressing harmonic emissions is crucial for maintaining power quality in the context of increasing EV adoption.

2. The influence of electric vehicles on harmonic emissions

The influence of harmonics in EV charging systems is a significant consideration due to its potential effects on power quality and the overall stability of the electrical network. In this context, multiples of the AC power supply’s fundamental frequency are referred to as harmonics. EV chargers have the potential to produce harmonics with unwanted frequencies that vary from the typical sinusoidal waveform.

The problem of power quality in EV charging systems is one of the main effects of harmonics. Increased distortion from harmonic currents and voltages can cause voltage waveform distortion and can cause electrical equipment to overheat. The effectiveness of the power distribution network may be affected and other linked devices may be impacted by this distortion. Furthermore, harmonics may increase the system’s energy losses and lower its overall energy efficiency.

Effective mitigation requires an understanding of the specifics of how harmonics are created in EV charging systems. Harmonics are produced in part by the non-linear design of EV chargers, especially those that use power electronics for rectification and conversion procedures. Waveform distortion results from the sudden pulses of current drawn by these nonlinear loads. Retaliators and converters used in the charging process cause abrupt changes in current, which reintroduces harmonic currents into the grid. The charging EV process involves rectifiers and converters that introduce rapid changes in current, leading to harmonic currents being injected back into the electrical network.

Most studies emphasized the significance of the issue of harmonics, especially with traditional chargers. High harmonics could lead to decreased lifespans of distribution network components, such as transformers and cables [7]. These harmonics can have several consequences. Firstly, they can lead to voltage distortion within the electrical system, affecting the quality of power supplied to other devices and appliances connected to the grid. This distortion can cause disruptions and reduce efficiency in the operation of various electrical equipment. Secondly, the presence of high-frequency harmonics can result in increased losses within transformers and cables. This is primarily because these harmonics cause a non-uniform distribution of current and subsequently lead to additional heating in these components. Such losses can impact the overall efficiency of the electrical system. Lastly, the integration of EVs into the grid, with the associated harmonics, poses various challenges. These challenges include managing harmonic distortion levels, addressing imbalances in the system, ensuring proper voltage regulation, and mitigating potential losses in transformers. Addressing these issues is essential to maintain the reliability and stability of the electrical grid in the face of increasing EV adoption. Harmonics are introduced into the system by non-linear equipment, such as EV chargers, as illustrated in Figure 1.

Figure 1.

Harmonic distortion in which the waveform is made up of fundamental and 3rd harmonic [8].

Two basic measures have been developed to estimate the amount of harmonic distortion and develop mitigation solutions. Total harmonic distortion (THD), which measures the percentage of the Root Mean Square (RMS) of the harmonic frequency components concerning the fundamental frequency component for both voltage V₁ and current I₁, is the first of these measures. Here, as shown in Eqs. (1) and (2), V_h and I_h stand for the RMS values of various-order harmonics in voltage and current [9].

$${\mathrm{V}}^{\mathrm{THD}}=\frac{\sqrt{{\mathrm{V}}_2^2+{\mathrm{V}}_3^2+\dots +{\mathrm{V}}_h^2}}{{\mathrm{V}}_1}$$E1

$${\mathrm{I}}^{\mathrm{THD}}=\frac{\sqrt{{\mathrm{I}}_2^2+{\mathrm{I}}_3^2+\dots +{\mathrm{I}}_h^2}}{{\mathrm{I}}_1}$$E2

Total Demand Distortion (TDD) is the second measure for evaluating harmonic distortion [10]. The following formula is used to calculate TDD, where I_ref stands for the nominal current:

$$\mathrm{TDD}=\frac{\sqrt{{\sum }_{\mathrm{h}=2}^{\mathrm{n}}{\mathrm{I}}_{\mathrm{h}}^2}}{{\mathrm{I}}_{\mathrm{ref}}}$$E3

International standards prescribe specific thresholds for current harmonics. For example, the IEC 61000 standard establishes a 13% limit for THD, while the IEEE 519 standard specifies a 5% threshold for TDD. These standards serve as regulatory benchmarks to ensure that levels of harmonic distortion in electrical systems remain within acceptable ranges.

2.1 Voltage distortion

Harmonics can distort the voltage in the electrical system, affecting the quality of power supplied to other devices and appliances connected to the grid.

Simultaneous fast charging of multiple electric vehicles will result in voltage distortion surpassing permissible limits. As per the EN 50160 standard, the total harmonic distortion of the supply voltage, encompassing all harmonics up to the 40th, should remain below 8% [11]. The substantial current demands of fast charging significantly influence voltage quality, particularly at the connection point, emphasizing its critical role in ensuring voltage stability.

The modeling of the fundamental and h^th harmonic currents from the nonlinear load situated at bus i, which has real power P and reactive power Q, is expressed as follows:

$${\mathrm{I}}_{\mathrm{i}}^1=\left[\left({\mathrm{P}}_{\mathrm{i}}+\mathrm{j}{\mathrm{Q}}_{\mathrm{i}}\right)/{\mathrm{V}}_{\mathrm{i}}^1\right]$$E4

In Eq. (5), R(h) represents the ratio of the h^th harmonic current to its fundamental counterpart

$${\mathrm{I}}_{\mathrm{i}}^1=\mathrm{R}\left(\mathrm{h}\right){\mathrm{I}}_{\mathrm{i}}^1$$E5

The harmonic voltages are determined by solving the following load-flow equation and consequently [8], the voltage at bus i is defined as shown in Eq. (7)

$${\mathrm{Y}}^{\mathrm{h}}{\mathrm{V}}^{\mathrm{h}}={\mathrm{I}}^{\mathrm{h}}$$E6

$$\mid {\mathrm{V}}_{\mathrm{i}}^{\mathrm{h}}\mid ={\left(\sum _{\mathrm{h}=1}^{\mathrm{H}}|{\mathrm{V}}_{\mathrm{i}}^{\mathrm{h}}|2\right)}^{\mathrm{1/2}}$$E7

2.2 Transformer and cable losses

The presence of high-frequency harmonics can lead to increased losses in transformers and cables. This is because these harmonics cause non-uniform current distribution and result in additional heating.

One of the challenges associated with EV battery charging comes from the potentially high harmonic currents associated with the conversion of AC power system voltages to DC EV battery voltages. Improvements in EV battery technology and government incentives will potentially contribute to higher EV penetration. Despite the advantages of this green technology, battery charging current harmonics injected into the grid incite an increase in transformer losses, followed by its temperature rise and lifetime reduction. The performance and ability of distribution transformers suffer under non-sinusoidal load operation, resulting in a lower power factor and quality [12].

The level of current harmonics circulating in a transformer winding can affect its operating temperature and lifetime. Although the existing standards mainly consider the impact of harmonics up to 2 kHz, higher frequency harmonics generated by high-power converters utilized in renewable energy sources can also contribute to the temperature rise of a transformer. Pulse Width Modulated voltage generated by power converters can generate significant high-frequency harmonics at its switching frequency. The switching frequency of converters in high-power applications is mainly between 2 and 9 kHz [13].

The transformer load P_L including current harmonics is presented in P_EC as the eddy-current loss, and P_S is the other stray loss. The harmonic loss factor, F_L, is applied to the winding eddy loss to indicate the heating due to harmonic load current and determine the transformer capabilities when supplying power to a load.

The harmonic loss factor for other stray losses, F_HS is employed to represent the heating impact as a result of other stray losses in liquid-filled transformers I² is the rms current [14].

$${\mathrm{P}}_{\mathrm{L}}={\mathrm{I}}^2\left(1+{\mathrm{P}}_{\mathrm{EC}}{\mathrm{F}}_{\mathrm{L}}+{\mathrm{P}}_{\mathrm{S}}{\mathrm{F}}_{\mathrm{HS}}\right)$$E8

Table 1 summarizes the various studies and their findings related to the impact of current harmonics on transformers, particularly in the context of EV chargers and nonlinear loads.

Electrical systems and transformers studies	Harmonics findings	Impact on transformer
Transformer losses and heat [15]	Current harmonics induce heat, causing thermal stress. 50% of transformer loss of life attributed to nonlinear loads.	Reduced lifespan due to heat stress.
Grid-connected inverters [16]	Experiment: Inverters generate low-order current harmonics (<2 kHz) leading to a 1.2°C insulation temperature increases at the rated load.	8.3% reduction in expected lifespan at rated load.
EV charger harmonics [17]	Assessment of EV chargers: harmonic loss factor predicts a significant potential decrease in transformer lifespan if the EV charger load exceeds 80% of the rated load.	Potential lifespan reduction with high EV charger load.
Industrial system load currents [18]	Simulation results: with approximately 80% nonlinear load, the transformer aging acceleration factor reaches about 2.97, indicating a significant reduction in its lifespan.	Notable lifespan reduction with high nonlinear load.
EV home chargers and power quality [8]	Study of EV home chargers: quadratic relation found between Total Harmonic Distortion (THDi) and transformer life consumption. Recommended THDi threshold of 25–30% for acceptable increase in life consumption.	THDi impacts transformer lifespan.
EV charger harmonics and distribution capacity [19]	Study on distribution system capacity: results indicate the 10 kV cable overload at 27.25% EV charger penetration due to harmonics, compared to 30.74% without harmonics. Suggested solution involves adding filters to EV chargers.	Distribution capacity and overload management.

Table 1.

Effects of harmonics on transformer performance and electrical system.

It’s noteworthy that underground cables are more susceptible to the impacts of EV-related harmonics compared to overhead transmission lines. Consequently, this area necessitates more stringent requirements and standards for charging stations. During the charging process, the maximum values of harmonics in cables consistently exceed those in overhead transmission lines. This discrepancy primarily arises from the lower surge impedance of cables compared to overhead lines, attributed to the closer proximity of conductors, which increases capacitance and reduces inductance [20].

2.3 Battery conditions

In order to carefully manage the energy transfer between various powertrain subsystems and guarantee the delivery of necessary torque and power to the vehicle’s wheels, EV powertrains heavily rely on power electronic components and electric machinery. Notably, along the powertrain’s direct current bus, these power subsystems have the potential to produce unwanted electrical harmonics. As a result, in addition to the basic DC current, the battery of the EV may be subjected to unfavorable oscillations that appear as both high- and low-frequency current variations. On the high voltage DC bus of EVs, empirical testing under real-world circumstances has revealed significant current harmonic disturbances ranging from 50 Hz to 4 kHz. Comprehensive studies have been conducted to understand the effects of these harmonics on the degeneration of battery systems within the small body of available literature [21].

3. Enhancing power system grid resilience

The overall relationship between power systems and grids takes center stage when examining the integration of electric vehicles. The power system, includes the generation, transmission, and distribution of electricity, while the power grid specifically refers to the interconnected equipment facilitating this energy transfer. The dynamic interaction between these components becomes crucial as EV adoption picks up speed. Aligning the grid with the changing EV landscape requires careful station location, smart charging algorithms, and the incorporation of renewable energy sources. Maintaining power quality and grid stability simultaneously requires tackling harmonic issues brought about by nonlinear loads from EV chargers. In order to create an integrated framework that guarantees the smooth integration of EVs into current power infrastructures, utilities, regulators, and technology developers must cooperate together.

Harmonic losses in the grid system affect energy efficiency because they raise resistive losses, which lower the total power factor. Higher generation capacity may be required to meet demand if there is a decline in the effective power provided to the loads as a result of a reduced power factor. As a result, the grid infrastructure is strained and might need to be upgraded to handle the increasing demand for EV charging.

Ensuring the reliability and dependability of energy infrastructure is critical, particularly concerning electric vehicles, requiring for enhancing the energy system grid’s resilience. In the era of electric vehicles, improving grid resilience is a complex problem that needs a variety of technological, governmental, and policy solutions. These techniques can be used to build a more enduring and efficient power supply that can support the increasing number of electric vehicles while enduring interruptions and disturbances.

To achieve this, it is crucial to take into account a variety of network reliability techniques and strategies, the most crucial of which are:

1. Developing the current grid infrastructure: electrical network modernization by integrating many advanced technologies such as sensors, smart meters, and automation to monitor and control the network more effectively. This allows for faster response times during outages and improve load management, even as demand for electric vehicle charging increases. One of the pivotal aspects of strengthening the electrical grid infrastructure is enhancing the cybersecurity of the grid in order to protect against cyber threats that may disrupt the energy system.

2. Solutions for power outages: ensuring continuous electric vehicle charging during power outages requires the implementation of three strategies. Firstly, the adoption of distributed energy resources, such as photovoltaic systems and small-scale wind turbines, enables local energy generation and storage. Secondly, by establishing small grids within communities, especially in areas exposed to severe weather events, to generate, distribute and consume energy locally. Electric vehicles can play a role in these microgrids by acting as mobile energy storage units and energy sources. Thirdly, equipping charging stations with backup power sources like batteries or generators, and integrating this with a grid resilience strategy. These strategies ensure uninterrupted EV charging and reduces reliance on the main grid during power outages, thus enhancing overall resilience.

3. Government regulations and public awareness: grid resilience should be prioritized while regulatory frameworks should support the seamless integration of electric vehicles into the grid. This can be done by encouraging investments in cutting-edge fast-charging station technologies and grid modernization. To reduce grid stress, regulated and responsible charging behaviors must be encouraged. Public awareness about the importance of proper charging behavior during grid stress or power outages. Mobile applications that provide information on grid stress times may be created by local authorities to help educate electric vehicle owners.

Moreover, when considering the grid’s size, the harmonics add complexity to the process of figuring out the right capacity and layout. Harmonic currents have the potential to overload transformers and conductors, which might affect sizing calculations that are typically based on linear load assumptions. Because harmonics are not sinusoidal, the sizing parameters need to be reconsidered in order to ensure that the grid infrastructure can accommodate the additional demand from EV charges without affecting reliability.

4. Harmonics emissions with charging rate

Harmonic emissions are impacted by a number of charging-related issues for electric vehicles. Various elements, including as charging rates, power distribution, and usage patterns, might be considered operational parameters. The management of harmonics in EVs is aided by the identification of probable correlations and their implications through the analysis of these parameters. For the purpose of creating management or mitigation methods for harmonics, investigating these relationships is crucial. This section delves into a more detailed exploration of the influence of various operational parameters within EVs on harmonics and explains why it’s crucial to analyze these parameters for harmonics management.

The impact of charging rates, a critical operational parameter, on harmonics in the context of EVs warrants thorough investigation. The swiftness of the charging process, particularly in fast-charging scenarios, is a subject of notable concern. While fast charging is instrumental in expediting the adoption of EVs, it introduces rapid fluctuations in power demand, which may engender harmonics and voltage variations. Fast charging, with its abrupt power demand shifts, can be a source of harmonic distortions and may lead to substantial voltage perturbations and losses [22].

The incorporation of electric vehicles primarily occurs within residential and commercial settings, and the speed of charging can potentially pose challenges related to harmonic distortion [6]. Several studies investigate both voltage and current harmonics, placing specific emphasis on the fast-charging process, particularly when it occurs within a cluster of chargers interconnected to the same electrical feeder [23]. The study cited in reference [24] observed a total harmonic distortion in the current from fast charging stations, which reached 32%.

When compared to regular or slow charging, fast charging entails much faster charging rates. This indicates that during the charging process, the power usage changes quickly and significantly. The electrical system may be subjected to harmonics as a result of these quick power shifts. While the low EV penetration levels with typical charging rates will result in acceptable harmonic levels [25].

To improve these issues, the adoption of standard charging protocols or the implementation of intelligent charging systems capable of adjusting charging rates in alignment with the grid’s capacity have demonstrated efficacy in mitigating harmonics. Moreover, a comprehensive analysis of the influence of these fast-charging stations on both low and high-order harmonics becomes imperative. This stems from the fact that the chargers utilized in these stations possess the potential to introduce harmonics into distribution networks at varying harmonic orders, necessitating a comprehensive analysis of the impact on the grid’s harmonics.

5. Managing harmonics and mitigation

Addressing higher harmonics, which are multiples of the fundamental frequency, can be relatively straightforward. By using active or passive filters or by incorporating suitable modulation techniques into the management of power electronics switches, these problems can be solved. These techniques work well to decrease higher harmonics’ negative influences on the power system. In contrast, extra complexity is introduced when dealing with lower harmonics, like the third, fifth, seventh, eleventh, and comparable orders. It is a difficult task to filter out these lower harmonics while preserving the integrity of the primary frequency signal. Because of their close closeness within the frequency spectrum, it becomes difficult to differentiate lower harmonics from the fundamental frequency. There are methods for canceling out lower harmonics, but they often come with practical and financial challenges. Harmonic cancellation methods, though available, tend to be neither cost-effective nor straightforward to implement from a technical standpoint [26].

Using an Active Power Filter APF to mitigate the harmonics produced by the EV charging station is a practical approach, given the difficulties in lowering harmonics from an EV charger that depends on passive power factor correction. Because they are more widely used than series APFs, shunt APFs are the better alternative. This is mainly because of their well-established, mature technology and ease of installation [27]. Uncontrolled high-speed charging caused the THDv to increase to 11.4%, above the recommended 8% limit, a solution to the harmonic problem was proposed by using the control of PV inverter as an active filter [28].

In certain research studies, it was proposed that the utilization of a smart charger can lead to a substantial reduction in THD when compared to conventional chargers. For example, in a study referenced as [29], the smart charger was found to draw sinusoidal current and maintain a unity power factor. Typically, ultra-high frequency switching is used by some inverters to lower emissions of harmonic distortion. To improve their chargers, manufacturers could include power factor correction circuits in the rectification stage. These circuits could use filters and pulse width modulation (PWM) techniques to handle harmonic issues [30].

Combining these approaches can result in a robust and effective system for EV chargers that effectively reduces harmonic distortions and ensures the health of the power distribution network as a whole. Additionally, smart grid solutions can further enhance communication between chargers and the grid. This will allow for intelligent charging scheduling. Research and development should be supported through educational programs, standards compliance, and regular system audits to ensure harmonic health and encourage the development of innovative harmonically friendly charging methods.

6. Conclusions

The integration of electric vehicles into the grid can pose challenges related to harmonic distortion levels, imbalances, voltage regulation, and potential losses in transformers. Harmonic distortion in electrical systems is a well-known concern, as it results in waveforms that deviate from the ideal sinusoidal pattern. The increasing use of non-linear power electronic devices and the proliferation of sensitive electronic loads have raised significant issues related to the safety and the reliable operation of electronic equipment. EVs emit harmonics due to their non-linear charging behavior, and these harmonics can impact the quality and efficiency of the electrical grid and connected devices. Managing and mitigating these harmonics is a critical consideration in the widespread adoption of electric vehicles.

Most investigations have shown that using normal EV chargers frequently results in harmonic levels that are undesired. If these high harmonic values are not reduced, it may be damaging to the lifespan of the transformers and cables that make up the distribution network. However, the negative effects of charger-induced harmonics can be greatly reduced by utilizing well-thought-out design practices for EV charger circuits, efficient control strategies, and the integration of filters into the charger circuit. More studies are necessary to address the issues raised by fast charging stations. These efforts ought to concentrate on removing harmonic distortion emissions from chargers through the improvement of the filters that are integrated into these charging systems, specifically for the purpose of preventing low-order and high-order harmonics.

The infrastructure of EV charging stations needs to minimize harmonics strategically on a larger system size. In order to bring harmonic distortion into the permitted range, this includes carefully placing harmonic mitigation devices, such as filters. This proactive strategy is essential for maintaining the electrical grid’s stability and dependability, particularly in view of the increasing number of electric vehicles on the road and the harmonic issues they provide.

Acknowledgments

Makawi Diab Hraiz gratefully acknowledges the University of Cádiz for postdoc-toral support with a Margarita-Salas fellowship, funded by the Ministry of Universi-ties of the Government of Spain through the European Recovery Instrument “Next Generation EU”, of the European Union (Order UNI/551/2021, of 26 May).